The present invention relates to a technology for controlling a radiation tomographic imaging apparatus equipped with a radiation tube having a liquid bearing.
As a radiation tube installed in a gantry rotating section of a radiation tomographic imaging apparatus, there has been proposed a radiation tube based on a liquid bearing, i.e., a liquid bearing system (refer to Japanese Unexamined Patent Publication No. Hei 08 (1996)-212949 and the like). In the radiation tube of the liquid bearing system, a liquid metal lubricant has been used in a bearing of a rotor that supports an anode. In this type of radiation tube, as compared with a conventional ball bearing system, mechanical friction is remarkably reduced and the conductivity of heat from the anode to the bearing is improved, thereby making it possible to realize a long lifetime, miniaturization and a large heat capacity.
Meanwhile, generally, the rotation of the rotor of the radiation tube is started when the radiation tomographic imaging apparatus is started up, and is stopped when the radiation tomographic imaging apparatus is shut down. As shown in FIG. 5, in a liquid bearing type radiation tube, when a rotor is stopped, the anode side of the rotor is slightly lowered by its own weight and the side opposite to the anode of the rotor is slightly elevated. At this time, the inner edge portion of the rotor on the side opposite to the anode thereof is brought into contact with the surface of a bearing. Thus, the inner edge on the side opposite to the anode of the rotor makes contact with the surface of the bearing on its gravity direction side while rotating at the moment when the rotating rotor is completely stopped, so that its contact portion is slightly damaged. The bearing is normally fixed to a housing for the radiation tube. Therefore, if a rotational angular position of a gantry rotating section at the time of the stop of the rotor is always the same, the portion of the bearing on its gravity direction side, i.e., damaged portion becomes always the same, thus resulting in shortening of the life of the bearing.
Incidentally, there has been disclosed in Japanese Patent No. 4678964, a method of changing on every occasion, a rotational angular position where a gantry rotating section is stopped, when a radiation tomographic imaging apparatus is shut down.
On the other hand, when the radiation tomographic imaging apparatus is shut down, the gantry rotating section is desirably stopped at a rotational angular position, a so-called home position to stop it when no scan is done, because of various reasons.
For example, the radiation tomographic imaging apparatus is often generally configured such that when the gantry rotating section is being stopped at the home position, a positioning light installed in the gantry rotating section is placed in a proper position to perform alignment of a subject. In this case, when the radiation tomographic imaging apparatus is shut down, the gantry rotating section is desirably stopped at the home position in such a manner that the subject alignment can be performed even immediately after the radiation tomographic imaging apparatus is restarted up.
Also, for example, the radiation tomographic imaging apparatus can be configured in such a manner that when the gantry rotating section is being stopped at the home position, the radiation tube and its heat exhausting unit provided to a gantry housing section most approach each other and the heat exhaust of the radiation tube is efficiently performed. The heat exhaust of the radiation tube is performed to suppress damage due to the heat storage of the radiation tube and shorten a waiting time till the radiation tube is cooled quickly to enable scanning. In such a case, it is desirable to stop the gantry rotating section at the home position in such a manner that the heat exhaust of the radiation tube is effectively performed when the scan is not done. Further, when the radiation tomographic imaging apparatus is shut down, the gantry rotating section is desirably stopped at the home position such that the heat exhaust of the radiation tube is started quickly when the radiation tomographic imaging apparatus is restarted up.
Further, for example, the radiation tomographic imaging apparatus can be configured in such a manner that when the gantry rotating section is stopped at the home position, a detector and its heat retaining unit provided to the gantry housing section most approach each other and the heat retention of the detector is performed efficiently. The heat retention of the detector is mainly performed to stabilize the detection property of the detector and stabilize the quality of a reconstructed image. In such a case, when the scan is not performed, the gantry rotating section is desirably stopped at the home position such that the heat retention of the radiation tube is effectively performed. Further, when the radiation tomographic imaging apparatus is shut down, the gantry rotating section is desirably stopped at the home position such that the heat retention of the radiation tube is started quickly when the radiation tomographic imaging apparatus is restarted up.
The following radiation tomographic imaging apparatus can be imagined regarding a temporary stop position and the home position. When the radiation tomographic imaging apparatus is shut down, the operation of rotating the gantry rotating section to the set rotational angular position and temporarily stop the gantry rotating section, and thereafter rotating the gantry rotating section again after a while and returning the same to the home position is performed.
With this situation in view, there has been a demand for a technology capable of shutting down a radiation tomographic imaging apparatus equipped with a radiation tube having a liquid bearing without shortening the life of the radiation tube and in safety.